Amplifiers are necessary in order to create a higher power signal from a lower power signal. A common application of an amplifier is to take an audio signal such as a voice or music signal and to amplify the signal to a power suitable to drive one or more speakers. For instance, many audio systems take information from sources such as compact disks, create a low power audio signal from the information, and amplify the information for presentation on speakers. Similarly, mobile devices such as cellular phones also take voice, music, or movie audio information and amplify the audio information for presentation on an internal or external speaker.
Amplifiers are typically grouped into “classes”. For instance, class-A, class-B, and class-AB amplifiers have been used for quite some time. These classes are met by analog amplifiers. One detriment to these types of amplifiers is a relatively low efficiency. For example, class-A amplifiers have a maximum theoretical efficiency of only 50 percent, while class-B amplifiers have a maximum theoretical efficiency of around 78 percent. These efficiencies can be suitable for certain audio systems, such as used in a home, but are typically too inefficient for use in portable systems, where battery life is important.
A relatively recent addition to amplifier classes is the so-called “class-D” amplifiers, which are switching amplifiers. Class-D amplifiers have become popular because their theoretical power efficiency is 100 percent and practically they can reach over 90 percent efficiency. Such amplifiers are therefore more suitable to portable systems, although they are not limited to such systems. In fact, many home theater amplifiers are made from class-D amplifiers.
While class-D amplifiers have benefits including high efficiencies, these amplifiers could still be improved.